Many modes of transport, in particular aircraft and high-speed trains, are generally made pressure-tight and aerated artificially. Aircraft have a pressurized cabin in which, at cruising altitude, a cabin pressure above the outside air pressure is established.
The air is supplied to a pressurized cabin usually both by means of circulation and purification of cabin air as well as by mixing in fresh air introduced from outside. Since the outside pressure at cruising altitude is below cabin pressure, the fresh air to be introduced has to be compressed. As a rule for the fresh air feed, some of the airstream from the compressor of one or more aircraft engines (so-called bleed air) is diverted, cooled to a desired temperature level and mixed in with the cabin air.
The bleed air from jet engines can be contaminated with oil residues or oil mists, particularly if, for example, lubricating oil in the engine escapes in the region of the axle or the like and is entrained by the compressor airstream. The oils from jet engines can contain constituents or additives that are harmful to humans, such as, for example, tricresyl phosphate (TCP). Entrained oil residues can also lead to an unpleasant smell of oil in the aircraft cabin. Recirculated cabin air can likewise contain odorous substances or harmful substances.
In the prior art it is therefore already known to provide filter systems for the bleed air of engines and/or recirculated cabin air. Firstly, activated carbon filters, for example, are known from prior public use. These have only a relatively low absorption capacity and bind harmful substances by means of physisorption in a reversible manner, meaning that said substances can also be released again in the event of relatively high loading of an activated carbon filter.
It is also known to remove undesired constituents from cabin air by catalytic oxidation (for example US 2003/0188850 A1, US 2009/0227195 A1, US 2010/0158775 A1 and US 2005/0053515 A1). Such catalytic systems are very complex to install and operate since operating conditions have to be constantly observed that permit catalytic oxidation of the harmful substances, for example temperatures of more than 200° C. for thermal catalysis or introduction of UV radiation for photocatalysis. WO 2013/124168 A1 discloses filter granules for filtering respiratory air in commercial aircraft.